FIG. 1 shows a configuration of a drive circuit using a heretofore known technology. In the drawing, EP represents a forward biasing power source, EN a reverse biasing power source, Tr1 a forward biasing switching element, Tr2 a reverse biasing switching element, R1 a forward biasing gate resistor, and R2 a reverse biasing gate resistor. A final-stage driver circuit DCC is a circuit for driving the MOSFETs Tr1 and Tr2 in accordance with a control signal. Herein, an IGBT (IGBT 1) is used as a semiconductor device. MOSFET is an abbreviation of Metal Oxide Semiconductor Field Effect Transistor.
With this kind of configuration, when a short circuit breakdown occurs in the semiconductor device, there is a high possibility of a short circuit breakdown occurring between all terminals G1, C1, and E1 of the IGBT 1. For this reason, in the case of FIG. 1, when there is a short circuit condition between the gate terminal G1 and emitter terminal E1, the output of the drive circuit connected between these terminals is short-circuited, a large current determined by the forward biasing power source EP and forward biasing gate resistor R1 continues to flow when the MOSFET Tr1 is turned on, and a large current determined by the reverse biasing power source EN and reverse biasing resistor R2 continues to flow when the MOSFET Tr2 is turned on. With the circuit type of FIG. 1, when taking into consideration the breakdown of the semiconductor device, it is essential to design in such a way that this kind of current can be tolerated, so the capacities of the biasing power sources EP and EN and gate resistors R1 and R2 through which the current flows increase, leading to an increase in size and an increase in cost of the drive circuit. Furthermore, when the drive circuit power source is shared, there also occurs a problem in that an overcurrent in one drive circuit renders another drive circuit inoperative.
As a heretofore technology that ameliorates this kind of problem, the method shown in FIG. 2 shown in Patent Document 1 is known. EP represents a forward biasing power source, EN a reverse biasing power source, Tr1 a forward biasing switching element, Tr2 a reverse biasing switching element, R1 a forward biasing gate resistor, and R2 a reverse biasing gate resistor. Also, F1, F2, and F3 represent fuses, SW1 represents a forward biasing power source short circuiting switch, and SW2 represents a reverse biasing power source EN short circuiting switch.
A description will be given of actions in this circuit when a short circuit breakdown occurs in an IGBT, which is a semiconductor device. When an IGBT 1 short circuits, and a large current flows through a collector, the fuse F1 melts down. Means of detecting a meltdown being provided in the fuse F1, when a meltdown is detected, the switches SW1 and SW2 are turned on. When these switches are turned on, the biasing power sources EP and EN are short circuited via the fuses F2 and F3, and the fuses F2 and F3 melt down. Owing to these kinds of action, the biasing semiconductor switches Tr1 and Tr2 are cut off from the biasing power sources in a short time, meaning that the large current in the drive circuit that occurs in FIG. 1 does not occur.
Patent Document 1: JP-UM-A-6-88191